Shirred food casings of flexible tubing are used in the meat industry for making sausage products such as frankfurters, pork sausages or the like. Typical materials for forming flexible tubing used for food casing include, among others, collagen, alginate and cellulosic material such as cellulose esters, cellulose ethers and regenerated cellulose, as well as other natural, synthetic or artificial materials. The casings are first prepared as hollow, thin-walled tubes of lengths ranging from about 12.2 to about 48.8 meters or more, and then shirred and longitudinally compressed to produce what is commonly termed in the art "shirred casing sticks" or "strands" which range in length from about 20 centimeters or less to about 55 centimeters or more. The ratio of casing length to the length of the shirred casing stick depends on several factors including the diameter of the casing. However, ratios in the range of 80:1 to 125:1 are common.
Shirred sticks, particularly of regenerated cellulose, are coherent in that the pleats formed by shirring and compressing nest one against another so the stick can be handled by mechanical means without disassociation of the pleats one from another.
Automatic machines have been developed for stuffing and linking shirred casing sticks with food emulsions to produce such products as frankfurters or the like on a continuous basis. One such automatic machine, disclosed in U.S. Pat. No. 3,115,668 to Townsend, is capable of successively stuffing and linking a shirred casing with food emulsion to produce a plurality of food links on a continuous basis. In an automatic stuffing operation using apparatus of the type described in the U.S. Pat. No. 3,115,668 Patent, the shirred sticks of casing, which are hollow, are fed automatically onto a stuffing horn by holding the stick and advancing the stuffing horn through the bore of the hollow stick. The horn moves the stick into a chuck which grips the fore end of the stick and rotates the stick about the stuffing horn. Food emulsion then is introduced into the casing causing the casing to fill and deshirr from the stick. The stuffed casing, which also is rotating, draws forward from the rotating stick and enters the grip of a continuously operating linker. This linker pulls the stuffed casing forward and cooperates with the chuck to form the filled casing into links of predetermined length.
Stuffing-linking machinery that operates in such a manner requires shirred food casing sticks to have a plug or closure at the fore end of such sticks. It is conventional practice to provide a casing stick with an end closure prepared as an operation of the shirring machine during the formation of the casing stick.
In general, end closures or "plugs" prepared in this fashion utilize a length of the casing which is turned into the stick bore and compressed to plug the fore end of the stick bore. The end closure or "plug" formed by this inturned casing performs several functions. For example, the stuffing horn which advances into the stick bore pushes on the plug for moving the entire stick towards the rotating chuck. Once the stick fore end is firmly gripped by the chuck, the horn, which continues to advance, pushes the plug out of the stick bore and into the linker just as stuffing starts.
Another function of the plug is that it closes the casing so it can be stuffed with emulsion. In this respect, the plug must be sufficiently coherent to contain the pressure of the stuffing operation until a first link is formed. Various types of casing closures, and methods for forming the same, have been disclosed in which casing from one end of the shirred stick is turned into the stick bore and compressed as for example, in U.S. Pat. Nos. 3,274,005; 3,383,222; 3,419,401; 3,892,869 and 4,759,100 among others.
In general, compressing the inturned casing is accomplished by locating a back stop against one end of the stick bore and inserting a tamp rod into the other end so as to compress the inturned casing between them.
Preferably, the closure formed of inturned casing contains as short a length of casing as possible. Using an excessive amount of casing from the shirred stick to form the closure means that less casing material is left in the shirred stick for stuffing. Conversely, if too little casing is used, the resulting end closure may not contain the pressure of food product being stuffed into the casing so the plug opens resulting in a "blown end" which allows the stuffing emulsion to spew from the casing.
It is important that the closure should not be too tightly anchored in the bore of the shirred stick or the surrounding casing could tear or otherwise break as the tightly anchored closure is forced from the fore end of the casing stick. If the plug is too firmly anchored in the stick bore, the force required to push the plug from the bore (hereafter referred to as the "deplug force") can exceed the tensile strength of the stick. Should this happen, the stick will lose its integrity and pleats will separate into two pieces of shirred casing connected by a length of deshirred casing. The connecting length of deshirred casing is liable to twist around the horn and cause the stick to seize on the horn. Another possible result of a high deplug force is a tearing of the casing or a "torn end" which also allows the stuffing emulsion to spew from the casing.
If the closure is too loosely anchored, a pressure rise within the stick bore, caused by compressing the air between the plug and the advancing stuffing horn, may cause the plug to eject from the bore and into the linker. This causes the linker to grip and pull casing forward before the emulsion flow starts so the first links formed may not be fully stuffed or may contain only air. Also, a compressed closure or plug which is loosely anchored in the stick bore tends to elongate over time. This is not desired because even if it remains in the bore until pushed out by the stuffing horn, the longer length may be gripped and pulled by the linker before the emulsion flow starts.
The degree of compaction is one factor which determines whether the closure is tightly or loosely anchored in the stick bore. This is because when the inturned casing is compressed between the tamp rod and back stop, the plug surface is formed by pressing the casing against the bore wall. The degree of compaction needed for retaining the stuffing pressure can be reduced if the length of the inturned casing is increased, but this is not desired as it decreases the amount of casing available for stuffing. Using less casing for the plug generally means that the degree of compaction must increase to provide a dense structure able to contain the stuffing pressure. However, for a given length of inturned casing, increasing the compaction increases the deplug force.
The patents noted above illustrate that various means have been proposed and used for automating the formation of end closures. Each has been successful to some extent but improvements are still desirable. In particular, it is desirable to provide an end closure which contains sufficient casing and is compacted to such an extent that it is effective to contain the stuffing while not being too tightly anchored in the stick bore, i.e. with a lower but still adequate deplug force.
Accordingly, one object of the present invention is to provide a new and improved apparatus and method of closing the fore end of a shirred casing stick.
Another object is to provide a method and apparatus for forming an end closure within the stick bore by longitudinally compacting a section of inturned casing within the stick bore such that only a portion of the end closure is formed against the bore wall.
Still another object is to provide a shirred casing stick having a new and improved end closure disposed and formed in the stick bore from casing drawn from one end of the stick.
A further object is to provide a shirred casing stick having a longitudinally compressed end closure disposed at one end of the stick bore wherein the end closure has only a portion of its surface formed and pressed against the bore wall.